Fuel injectors are conventionally used to provide a measured flow of fuel into an internal combustion engine. In the case of direct injection systems, a high-pressure injector extends into the combustion chamber. Consequently, a downstream face of the fuel injector's seat is prone to the formation of combustion chamber deposits. It is desirable to minimize this formation of deposits in order to maintain the intended operation of the fuel injector.
For the intended operation, it is critical for the seat to provide a sealing surface for engaging a displaceable closure member, e.g., a needle of a conventional fuel injector assembly. In a first position of the closure member relative to the seat, i.e., when the closure member contiguously engages the seat, fuel flow through the injector is prohibited. In a second position of the closure member relative to the seat, i.e., when the closure member is separated from the seat, fuel flow through the injector is permitted.
In order to provide the sealing surface, it is known to provide the seat with a conical portion having a desired included angle. Conventionally, grinding tools with a conical shape are used to grind the conical portion. It is also known that the quality of a surface finish is related to the grinding velocity. In the case of conical shape grinding tools, the grinding velocity decreases toward the apex of the tools.
In the case of fuel injector seats having a small orifice, the velocity of the grinding tool at the edge of the orifice is insufficient. Thus, conventional grinding operations cannot provide a selected finish on conventional conical portions.